Interpretive Summary: Malignant catarrhal fever (MCF) is a devastating disease for American bison. It is becoming one of the most important infectious diseases for bison producers in North America. Virtually all bison MCF cases in North America are caused by ovine herpesvirus 2 (OvHV-2), a herpesvirus carried almost exclusively by sheep. In this communication, we report transmission of OvHV-2 from feedlot lambs to bison on a neighboring ranch that occurred at distances up to 3 miles. A total of 60 (7.9%) out of 761 bison developed MCF over a six-month period. The percent mortality from MCF in three different bison groups tracked over time on the ranch correlated with the initial distance from the lambs: 17.5%, 6.1%, and 0.43% at approximately 1, 2.6, and 3.2 miles, respectively. The study documented that OvHV-2 can be transmitted over a significant distance under certain conditions, that distance is an important factor in transmission efficiency, and that sheep feedlots are a significant source of virus for transmission.

Technical Abstract:
Malignant catarrhal fever (MCF) is potentially devastating to American bison. Virtually all bison MCF cases in North America are caused by ovine herpesvirus 2 (OvHV-2), a member of the gammaherpesvirus subfamily, which is carried almost exclusively by sheep. In this communication, we report transmission of OvHV-2 from feedlot lambs to bison on a neighboring ranch that occurred at distances up to 3 miles. A total of 60 (7.9%) out of 761 bison developed MCF over a six-month period. The percent mortality from MCF in three different bison groups tracked over time on the ranch correlated with the initial distance from the lambs: 17.5%, 6.1%, and 0.43% at approximately 1, 2.6, and 3.2 miles, respectively. The study documented that OvHV-2 can be transmitted over a significant distance under certain conditions, that distance is an important factor in transmission efficiency, and that sheep feedlots are a significant source of virus for transmission.